Study: Response of Nodulation and Nitrogen Fixation to Salt Stress in a Desert Legume, Alhagi Sparsifolia
In desert ecosystems, plants are suffered from nutrient deficiency and salt stress. Legume shrubs and trees, capable of symbiotic N2 fixation, receive much research attention in applying for phytoremediation and ecological reconstruction in drylands. Estimates of nitrogen fixed by dryland perennial legumes vary greatly at the regional scale, generally being higher than those in the more humid regions. The nodulation and nitrogen fixation of Alhagi sparsifolia, a perennial deep-rooted legume naturally distributed in the transition zone of Taklimakan Desert and Qira oasis, showed a large variation in N2 fixation (foliar δ15N), and nodulated Alhagi plants have been found to down-regulate nitrate reductase activity (NRA) when compared to non-nodulated individuals. It is not clear if variation in N2 fixation and NRA is a genetic trait that varies across Alhagi populations, or if observed patterns are a plastic response of individual plants to environmental conditions.
Researchers from Cele National Station of Observation and Research for Desert-Grassland Ecosystem, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, examined the potential factors that shape the symbiotic nitrogen fixation of naturally growing Alhagi individuals at terminal ends of gradient change in the Taklimakan Desert, from high salinity riparian areas into low salinity desert sand dunes.
Researchers found that nodulation and N2 fixation in Alhagi plants is highly plastic in response to variation in soil chemistry (nitrate or salt concentrations), and found evidence supporting that this variation in N acquisition is not genetically based. BNF of Alhagi plants is more salt-tolerant than mineral nitrogen assimilation is, and this trait helps legume plants better adapt and colonize diverse habitats with differing resource availability and salt concentrations. The ecological importance of deep-rooted legumes in arid and semiarid ecosystems is receiving increasing attention due to global climate change and soil degradation worldwide. In addition to more commonly attributed services provided by legumes including improvement of soil fertility and increasing soil stability, high water use by Alhagi may provide salinization control by reducing the water table of shallow aquifers, which may be highly saline.
The study improves understanding of the response of nitrogen metabolism of deep-rooted legumes to environmental factors and nitrogen utilization strategies of these plants in drylands, and provides new insight on their important role in dryland regions. The attribute of deep-rooted legumes has an increasingly prominent role in bio-remediating areas affected by soil salinization by increasing soil productivity and improving soil structure.
Results of the study were published on Environmental and Experimental Botany, entitled "Response of nodulation and nitrogen fixation to salt stress in a desert legume, Alhagi sparsifolia".
Figure: Scatter matrix illustrating correlations between A. sparsifolia nitrogen fixation activity (δ15N) and environmental factors including Na+, Cl-, SO42-, Ca2+, K+, Mg2+, HCO3-, NO3-N, NH3-N, PO43-, pH, electrical conductivity (EC), gravity water content (GWC), groundwater depth (GD) and distances to the nearby river (DTR).
Contact: LIU Jie, Xinjiang Institute of Ecology and Geography